Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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- 1 - C-I-L 624
This invention relates to a chemical gas generating
composition in solid form capable, upon ignition, of rapidly
producing large volumes of non-toxic gases. The gas generating
composition of the invention is particularly adapted for in-
flating safety crash bags in passive restraint systems for
passenger vehicles.
The use of protective gas inflated bags to cushion
vehicle occupants in a crash situation is now widely known
and well documented. In the first devised systems of this
type, a quantity of compressed, stored gas was employed to
inflate a crash bag which upon inflation was imposed between
the occupant and the windshield, steering wheel and dashboard
of the vehicle. In response to rapid deceleration of the
vehicle, as in an accident situation, the gas was released
through a quick-acting valve or the like to inflate the
; crash bag. Because of the bulk of the apparatus, its generally
slow reaction time and its maintenance difficulties this
stored, pressurized gas system has now largely been superseded
by a system which utilizes the gases generated by the
ignition of a chemical gas generating pyrotechnic substance
or composition. Such a chemical system employs an ignition
means such as an electrically activated s~uib or the like
asssciated with a suitable sensing means to ignite the gas
generating composition.
:, .
7~
A large number of quic~-burning gas generating
compositions have been proposed for crash bag inflation
purposes, many of which have proven deficient ln one respect
or other. It has been a preoccupation of the industry to
develop a gas generating composition which combines the
essential features of a short induction period, a burn rate
which is rapid but without any explosive effect, a high bulk
density, so that only a small amount of composition is
required to produce large amounts of gas; the production of
only non-koxic gases, so that vehicle occupants are not
endangered in the event of a leak or during the venting of
the crash bag after development; the production of gases at
a relatively low temperature, so that damage to the crash
bag is minimized and occupants are not burned; good filter-
ability of the reaction products, so that hot solid residue
cinders are simply removed from tl~e gas stream; and strong
physical form, so that long period of storage can be attained
under wide ranging conditions of temperature cycling and
shock. While some or other of these desirable properties
are found in known chemical gas generating compositions,
heretofore it has not been possible to provide compositions
which satisfy all the requirements of the industry.
The most widely accepted prior art gas generating
compositions generally comprise a mixture or blend of an
alkali metal or earth metal azide, usually sodium azide, and
one or other of a selected oxidizer, commonly a metal oxide.
Sometimes a small amount of a burning catalyst is included
in the mixture to speed up the burn rate or reaction time.
In some cases the metal oxide is replaced by a metallic
chloride, nitrate, sulfate, peroxide, perchloride or other
oxidizer. A wide range of these selected combinations are to
be found in the patent literature. (See, for example, U.S.
patent numbers 2,981,616, 3,122,462, 3,741,585, 3,755,182,
3,773,947, 3,779,823, 3,895,089, 3,806,461, 3,833,432, 3,912,561,
3,883,373, 3,996,029, 3,391,040 and 4,062,708).
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In all of the aforementioned patents the search
has been clirected to providing a composition which combines
safety, low cost and gas generating effectiveness. ~lith
the advance of technology in the field of vehicle air bags
systems, an ever increasing desire has been expressed for
a gas generant of yet further improved performance in terms
of ease of ignition, filterability, improved burn rate and
reduced costs. Some distance in the direction of improved
performance has been gained by the addition to known
formulations of further oxidizers such as, for example, NaN03
or KC104. However, while the addition of these materials
increases the composition burn rate, they also tend to
undesirably increase flame temperature and to increase the
production difficult-to-filter particulates upon ignition.
Thus further improved performance within the limitations
of prior art knowledge heretofore has been deemed unlikely.
In the combustion of, for example, a stoichiometric
mixture of sodium azide and metal oxide, the reaction products
obtained may includa nitrogen, molten metal, sodium oxide,
sodium salt of the metal and metal nitride. One or other or
several of these products are produced depending on the type
of metal o~ide selected. ~,enerally, the more reactive the
metal of the oxide the more numerous are the products
obtained. Because of the desire to reduce the amounts of
sodium oxide and metal nitrides and to increase the amounts
of nitrogen gas, the choice of metal oxide must be carefully
made. It has been found tha-t by a ~udicious selection of
a combination of metal oxides, a multi-ingredient gas
generating composition may be provided which can be tailored
to a system which has the desired ignitibility, burn rate,
gas efficiency, filterability, low hazard and low cost,
which system is eagerly sought by the industry.
It is an object o~ the present invention to provide
an improved solid gas generating composition which possess,
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in particular, a high degree of safety in handling and manu-
facture, a rapid burn rate together with a controlled flame
temperature, a very high level of gas cleanliness and a very
s low level of toxic ignition by-products.
The improved gas generating composition of the
present invention comprises one or more alkali metal azides
or alkali earth metal azides in admixture ~ith a stoichio-
metric amount of at least two metal oxides selected from
the group consisting of Fe2O3, SiO2, ~InO2, Ta2O5, Nb2O5
and SnO2.
For optimum results, the cOmpositions may opti~nally
contain a minor amount of a further metal oxide selected from
the group of Tio2, A12O3 and ZnO or mixtures of these.
The compositions of the invention demonstrate a
surprising synergism in that the actual measured properties
resulting from the use of a mixture of the selected metal
oxides are superior to the properties anticipated from a
simple mechanical mixture. In particular, ignition delay
time, pressure of the gases generated, burn rate, amount of
free sodium in the residue, dust after ignition and flame
temperature can be shown to deviate favourably from the
expected results as determined by calcula~ion.
The metallic azides suitable for use in the compositions
of the invention are the alkali metal and alkali earth
metal azides, in particular, sodium azide, potassium azide,
lithium azide, calcium azide and barium azide. The method
of manufacture of the gas generating compositions of the
invention is a simple one which merely re~uires the
combination of fine granular or powdered alkali metal or
alkali eàr~th metal azide and very fine particulate metal
oxides to thoroughly mix the ingredients. The resulting
combined ingredients may then be prepared in a suitable
physical form ~or use in air bag inflation such as in the
form of compressed pellets or tablets or as porous granules
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as disclosed in U.S. patent No. 3,996,079.
The following examples and tables illustrate the
improved properties and characteristics of the gas generating
composition of the present invention. In the examples and
accompanying text the various gas generant compositions or
formulations are designated by means of formulation labels
as indicated below:
0 Formulation Label Sodium azide/~5etal Oxide r~etal Oxide
molar ratio
F9 4/1 Fe23
SA 4/1 SnO2
~q 8/3 rlnO2
CA 4/3 SiO
TA 10/1 Ta225
z 4/3 ZnO
A 4/1 A123
TI 4/1 TiO2
The compositions in the following examples are designated and
discussed in terms of the above defined formulations.
EXAMPLES 1-2
To demonstrate the utility of the multi-component
gas generants of the present invention, a series of
25 compositions comprising stoichiometric mixtures of sodium
azide and at least two metal oxides were prepared and burned.
The performance results obtained were compared with
measured results from the burning of conventional sodium azide/
iron oxide mixtures. In all cases the compositions were in
30 the form of one inch diameter pressed pellets weighing 20
grams. The results are tabulated in Table I, below. F 9
composition is used in Example 1 while the composition of Example
2 comprises a mixture of F 9 and SA in a weight ratio F 9/SA
of 9:1.
.
~.~ 4~7S6
TABLE I
. ~ _~
Example 1 Example 2
NaN3/Fe203 NaN3/SnO2/Fe203
Pellet _
Density (g/ml) 2.127 2.101
Ignition delay 1041 525
tlme (ms)
max. (psi) 1371 1413
10 Burn rate as 2.04
(dlnP/dt) max.(s 1) 1.55
Na in cinder* 2 0
Dust in gas* 3
Flame temp. (C.)
calc. 1026 _
measured 990 _
Relative and based on a scale from 0-lQ
From Table I it can be seen that the Example 2
composition containing both tin oxide and iron oxide was
superior in all performance characteristics to the
conventional azide/iron oxide composition of Example 1. It
can be noted that the composition of Example 2 differs from
that of Example 1 by the incorporation of 10% SA composition.
EXAMPLES 3-5
A further series of multi-component gas generants
similar to those of Examples 1 and 2 were prepared except
that the form of the composition was that of extruded granular
particles each about 1.14 inch in outside and 0.04 inch in
inside diameter x 0.50 inch in length. ~uantities of 12 grams
of each composition were burned and the performance results
obtained were compared with those from the burning of
conventional azide/iron oxide mixtures. The results are
-- 7
tabulated in Table II below. In Example 3, the performance
of the F 9 formulation is shown. The compositions employed
in Examples 4 and 5 respectively comprise mixtures of CA and
~ in the weight ratio 1:2 (Example 4) and F 9: CA: M in the
weight ratio 3:1:3 (Example 5)
TABLE II
,
Example 3Example 4 Example 5
NaN3/Fe203NaN3/SiO2/ NaN3/Fe20
. rlno2r~n2/SiO2
Bulk
Density (g/ml) 1.0830.9980.994
Ignition delay
time (ms) 138 41 25
15 Generator pressure
max. (psi) 10222209 1530
Burn rate as
(dlnP/dt) max. (s 1) 9.9 101 66
Sodium in cinder 1 8 0
20 Dust in gas 5 1 1
Flame temp. ( C)
calc. 10261040 1064
measured 9C~837 1033
From Table II it can be seen that the compositions of
Examples 4 and 5 demonstrate vastly superior properties over
the conventional azide/iron oxide material of Example 3.
Particular attention is dlrected to the burn rate of the
composition of Example 4 which is greater by a factor of 10
than that of the conventional composition of Example 3.
EXAMPLES 6-7
To demonstrate a synergistic effect found with
the multi-component gas generants of the lnvention, the
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burn rate of a three-component generant was compared to the
burn rate of separate two-component generants employing the
same metallic oxides. The results are demonstrated in the
attached drawings, where
~ igure 1 shows the burn rate of extruded grains of
a generant comprising NaN3/Fe203/Ta205 and
Figure 2 shows the burn rate of extruded grains of
a generant comprising NaN3/Fe203/Ta205
The solid lines in the two figures indicate the
experimentally determined burn-rate dependence on composition
whereas the broken lines indicate the "expected" dependence,
in the absence oE a synergistic effect. The abscissa in Fig.l
gives the weight ratio of the formulas F9 and CA in the mixture.
That in Fig. 2 refers to weight ratio of F9 and TA formulas.
With particular reference to Figure 1 (Example 6),
the solid line shows the burn rate R with dependence on the
composition while the broken line shows the expected burn rate
R with dependence on the composition. The left hand margin of
the graph shows a scale of the rate of gas generated expressed
as (dlnP/dt) max (s 1) The vertical lines show the spread of
R-values. It will be seen by reference to Figure 1 that
compositions comprising less than 40% NaN3/SiO2 have
excellent burn rates in the range of 11 to 33 (s 1). This good
burn rate is achieved through an increase of flame temperature
resulting from the chosen mixture of ingredients, and, in
turn, augments gas production and generates an easily filter-
able cinder.
It may be mentioned that due to low bulk density
of the formula CA, the compositions containing more than 40
NaN3/SiO2 have a poor gas yield (per unit volume of the gas
generator) and are not of a practical use.
The optimum formula or blend chosen will be influenced
by the type and construction of the gas generator apparatus
employed.
- 9 -
With reference to Figure ~ (Example 7) there is shown
in broken line the expected or anticipated burn rate predicted
by additivity rule while the solid line shows actual experimental
results ~rom the burning of a multi-component yas generant.
The results demonstrate a surprising synergism,
particularl~ where the amount of NaN3/Ta2O5 in the mixture
is low. Thus it can be seen that the addition of relatively
small amounts of tantalum oxide to a conventional NaN3/Fe2O3
gas generant, significantly improved performance. Pure Ta2O5
is prohibitively expensive. However, due to close similarity in
atomic or ionic size, ionization and electrode Potential it shows
nea.rly identical chemical reactivity as its mixtures with
niobium. Tantalum is found in a nu~ber of ores invariably
containing niobium. Some of them, viz. tantalite or columbite
contain up to 92~ of (Ta,Nb)2O5 which can be successfully used
as substitute for Ta2O5 in Example 7.
EXAMPLE 8
To further demonstrate the synergism found in the
gas generants of the present invention, standard or conven-
tional two-component gas generants were burn-tested and the
performance parameters recorded. From the results obtained
the expected performance parameters of mixtures of the two-
component gas generants were calculated by algebraic averag-
ing and these expected results were compared with actualmeasured results from the burninq of one inch diameter, 20 g.
; pellets of the mixtures. The results are shown in Table III
below.
-- 10 --
TABLE III
r ~ : . ____ ~ . ._ . . ____ _ .
Parame-ter NaN / NaN3/ NaN3/Fe O3/SnO2
S Pellet ~e2O3 Sno2 E ~ d ~leasured
Density (g/ml) 2.127 2.221 2.136 2.101
Ignition delay 1041 533 990 525
time (ms)
Generator max. 1371 1304 1364 1413
lO pressure (psi)
Burn rate as
(dlnP/dt max.ts 1) 1.55 1.41 1.54 2.04
Free sodium in cinder
(relative) 2 2 2 0
15 Dust in the gas phase
(relative) 3 2 2-3
Flame temperature (C)
calculated 1026 921 _ _
20 measured __ .
From the results in Table III it will be seen that
the measured ignition delay time, gas pressure, burn rate and
residues of the three~component mixture were all superior to
the calculated, expected results.
EX~PLE 9
The synergism found in the gas generants of the
present invention was further demons~rated by comparing the
performance parameters of burned, extruded particles of
conventional two-component systems with the results obtained
from the burning of similar extruded three-component and
four-component mixtures. The results were contrasted with
the expected performance parameters calculated by algebraic
averaging. The results are tabulated in Table IV below.
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TA3LE IV
_ . . . . . . ._
Parameter S y s t e m
.. __ . _ .
NaN3/Fe203 NaN3/SiO2 ~JaN3/MnO2
,.. . .. . ~ . .. _ .. _ _
Bulk
Density (g,/ml)1.083 0.654 1.109
Ignition deLay138 12 118
time (ms)
Generator Maximum 1022 1036 966
~ressure (psi)
Burn rate as 19-9 8.5 9.8
(dlnP/dt) max (s )
Sodium in the 1 1 8
.~ cinder (relative)
: Dust in the gas5 3
:`: ~ iv_,
,
; Flame Temp. (C)1026 987
.~ calculated 990 998
measured
. . _
cont'd
,~
;``
:
~ : '
- 12 -
TABLE IV cont'd
.. . .. . . _
Parameter _ S y s t e m
Blends of NaN3/~lnO2
1) NaN3~`1nO2/ 2)NaN3/~lnO2/ 3)NaN3/MnO
2 _ _ SlO2 2/FeO3
Ex~. ~Meas. Exp. Meas. Ex~ ~leas.
Bulk ~ _ ~-
Density (g/ml) 0.9950.913 0.957 0.998 1.033 0.994
Ignition delay 10638 96 41 111 25
time (ms)
Generator Maximum 10251869 10272009 looo 1530
pressure (psi)
Burn rate as -1 9-580 9.4 101 9,7 66
(dlnP/dt)max(s )
Sodium in the 1 3 1 8 4 0
cinder (relative)
Dust in the gas 4 4 4 1 3 1
phase (relative)
~ _ _ . .... _ ,_ _ .
Flame Temp. (&)
calculated 1260 1040 1064
measured 959 837 1033
Notes: Compositions 1), 2) and 3) comprise the
following weight ratios of the two-component
mixtures, respectively.
1) M:CA ~ 3:1
2) M:CA ~ 2:1
3) ~I:CA:F - 3:1:3
It will be seen from Table IV that in all cases the
measured results from the burning of the multi-component
generants were superior to the expected, calculated results.
This is particularly evident in the burn rate measurements.
A particular problem facing the passive air bag
industry h~s been the development of effective, low cost
filtering means for the removal from the generated gas, prior
to bag inflation, of the residue or cinder carried in
the gas stream. r^lhere some of this residue is in liquid
form, for example, from molten metal, mechanical filters
tend to quickly become clogged and block free passage of the
gas. ~Thile the production of liquid residue may be controlled
through the use of cooler burning mixtures, this results in
an undesirable sacrifice in both burn rate and gas generating
efficiency. Hence it has been the desire of the industry to
utilize a high burn rate, high gas generating material while
maintaining an easy-to-filter residue. It has now been found
that the addition to a multi-component gas generant of a
secondary metal oxide selected from aluminium oxide, titanium
oxide and zinc oxide or mixtures of these, results in the
production of an easily filterable, semi-solid cinder without
sacrifice in performance of the generant. It has also been
found that the same secondary metal oxides, aluminium oxide,
titanium oxide and zinc oxide or mixtures of thereof, may be
added to simple or conventional two-component gas generants
to produce a similar, easily filterable residue. Generally,
the quantity of secondary metal oxlde empl.oyed as a residue
controller is no more than one part of secondary metal oxide
to one part of the primary metal oxide or oxides.
EXAMPLE lO
.
To demonstrate the improved quality of residue obtained
- by t:~e use of a secondar~ metal oxide, a stoichiometric
composition comprising sodium azide/silicon oxide/manganese
oxide was compounded in extruded grain form with and without
:
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- 14 -
the inclusion of the secondary metal oxide, titanium oxide.
Both compositions were ignited and the results obtained
are shown in Table V, below:
TABLE V
_ __ ~ _ ____ __ _ _ ___._ _._ _ ____.A__ ' . __ _
NaN3/SiO2/ NaN3/SiO2/
MnO2 I`lnO2/TiO2 *
_ .. ~ ...__ . . ..
~ensity 0.913 0.870
Ignition delay time (ms)38 117
Generator pressure (psi)1869 1580
Burn rate 80 44.2
Sodium in cinder (relative) 3
lame tempO (C) 959 960
rype of residue llqu~d semi-solid
*
The composition is a stoichiometric blend of
NaN3/SiO2/MnO2 and NaN3/~iO2/TiO2-
EXAMPLE 11
To demonstrate the improved cinder-forming properties
of a gas generating composition of the inventio~ containing
aluminium oxide as a secondary metal oxide, two stoichimetric
compositions were prepared. Composition CA comprised
sodium azide/silicon dioxide (4/3) while composition CA~
comprised the same composltion but 50 mole ~ of the silicon
dioxide was replaced by aluminium oxide. Both compositions
were prepared in identical poxous granular form and ignited.
The results are shown in Table VI below:
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TABLE VI
Property CA CAA
Bulk density (g/ml) 0.658 0.688
5 Ignition delay time (ms) 16 159
~,enerator pressure (psi) 99~ 1014
Burn rate (s ) 6.3 7.2
Crush strength (kg) 3.8 4.4
Sodium in cinder 1 4
10 Dust 4 4
Flame temperature (calc)(C) 978 818
Type of residue VlSCOUS liquid solid
~ . *
CAA is the same composition as CA but 50 mole % of SiO2
was replaced by A12O3.
It can be noted that substitu-tion of 50 mole % of SiO2 in
CA formula by A12O3 resulted in stronger grain, which burned
faster and at the same time cooler than CA. The reaction
products of CA~ were easy-to-filter solids.
EXAMPL~ 12
Two stoichiometric compositions were prepared, extruded
and tested as in Example 11. Composition A comprised a
mixture of sodium azide/manganese dioxide/silicon dioxide
: wherein the moles ratio of the two metal oxides was 1:1.
Composition B comprised a mixture of sodium azide/manganese
dioxide/aluminium oxide. The results are shown in Table VII
; below:
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- 16 -
TABLE VI I
~ . ._
Comp A Comp B
Property (with SiO2) (with A1203)
. .,...................... . _ . .
5 Bulk density (g/ml) . 913 1.103
Ignition delay time (ms) 38 106
Generator pressure (psi) 1839 1128
Burn rate (s 1) 80 19
Crush strength (kg) 3.8 5.3
10 Sodium in cinder 3 2
Dust 4 3
Flame temperature (calc)(C)1103 960
(measured) 959 820
Type of residue l~quid sem~-solid
:
15 The results in Table VII show that the incorporatlon of A12O3
improves the mechanical strength of the grains. The
composition containing A1203 burns cooler and slower than that
with SiO2. The cinder resulting from burning of Comp A was
a low-viscosity liquid which entirely penetrated the
20 filtering means. By contrast, the cinder of Comp B was
a white-water-soluble powder held back by the filtering means.
For optimious results for a compositin for use in a
vèhicle passive restraint system, a formulation lying
~ between that of Composition A and Composition B would
- 25 be selected. By appropriate selection of materials and
adjustment of the blends, a gas generant can be provided
having the desired burn performance.
